This invention relates to magnetic recording media such as magnetic disks, magnetic drums and magnetic tapes in which a layer of a magnetic recording material is formed on a substrate and is overlaid with a protective coating layer, and more particularly to the material and structure of the protective coating layer and method of forming that layer.
For storage of information for computers, so-called hard disks and floppy disks using a thin film of magnetic metal as the recording medium have very rapidly and widely spread in recent years, and to keep up with the trend toward such disk memories more enhancement of recording density is growingly required of each magnetic recording device. One way to enhance recording density is decreasing the magnetic head-to-recording medium spacings, and in this regard not only a reduction in the flying height of the magnetic head but also a reduction in the thickness of the protective film on the recording medium have become important tasks.
The protective film on the magnetic recording medium is required to be high in wear resistance to withstand the rubbing contact with the magnetic head at starting and stopping the operation of the recording device. Besides, corrosion resistance is required of the protective film to prevent the underlying magnetic film from corrosion particularly when the magnetic film is a metal film which is more susceptible to corrosion than a magnetic oxide film. In most of conventional magnetic recording media the protective film is formed of a stable and hard oxide represented by SiO.sub.2, and in some cases carbon is used as the protective material in view of its lubricity.
Regarding thinning of the protective film for the purpose of enhancing recording density, it is accepted that the protective film thickness has to be reduced to less than 50 nm to realize recording density of 50 kilobites per inch or above. However, it is very difficult to ensure mechanical durability and weatherability of the recording medium by a protective film of such a reduced thickness. Particularly in magnetic memories using a thin film of metal as the recording medium it becomes impracticable to completely prevent occurrence of bit errors attributed to corrosion by using a conventional material for the protective film.
U.S. Pat. No. 4,411,963 relates to magnetic recording media and proposes to overlay a magnetic metal film with a film of either corrosion resistant metal such as gold and/or tantalum or refractory carbide or nitride of, for example, silicon. However, the corrosion resistant metal film will be insufficient in wear resistance. In the case of a refractory carbide or nitride film, the film is very high in hardness and also in the coefficient of friction and, therefore, is likely to damage the magnetic head. In practice it will be necessary to apply a liquid lubricant to such a hard protective film. However, use of a liquid lubricant entails extra cost and offers disadvantages such as possibility of cohesion of the magnetic head and the protective film and accumulation of dust.